Tornadogenesis and Early Tornado Evolution in the El Reno, Oklahoma, Supercell on 31 May 2013

This study documents the formation and part of the early evolution of a large, violent tornado near El Reno, Oklahoma, based on data from a mobile, polarimetric, rapid scan, X-band, Doppler radar. The main circulation associated with the tornado formed near the ground initially, ~90 s prior to the d...

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Bibliographic Details
Published in:Monthly weather review 2019-06, Vol.147 (6), p.2045-2066
Main Authors: Bluestein, Howard B., Thiem, Kyle J., Snyder, Jeffrey C., Houser, Jana B.
Format: Article
Language:English
Subjects:
Cooling rate
Data collection
Datasets
Doppler radar
Doppler sonar
Downdraft
Echoes
Evaporative cooling
Evolution
Gust front
Lofting
Momentum
Precipitation
Radar
Radar data
Radar polarimetry
Reflectance
Rotation
Simulation
Storms
Superhigh frequencies
Thunderstorms
Tornadoes
Vortices
Vorticity
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Summary:This study documents the formation and part of the early evolution of a large, violent tornado near El Reno, Oklahoma, based on data from a mobile, polarimetric, rapid scan, X-band, Doppler radar. The main circulation associated with the tornado formed near the ground initially, ~90 s prior to the development of the vertically coherent vortex, which built upward through a vertical column of at least 3.5 km in less than 20 s, the update time of the Doppler radar data. Strong but broad rotation from 500 m to 1.5 km AGL also preceded the formation of the tornado at the surface by several minutes. A precipitation-loaded downdraft was observed in the right-forward flank of the storm, which could have enhanced evaporative cooling and allowed for a faster rate of baroclinic generation of low-level horizontal vorticity, while descending reflectivity cores in the right-rear quadrant might have enhanced low-level convergence to the rear of or along the leading edge of the rear-flank gust front. The intensification of the tornado occurred in spurts, not steadily, perhaps owing to surges in momentum at the surface associated with the precipitation-laden downdrafts. The tornado was highly tilted even when it was intensifying, calling into question the importance of a vertical juxtaposition of the mesocyclone aloft and the tornado at the surface. In this case study, while the development of a weak-echo hole was evidence of rotation, the absence of one did not mean that there was not a strong vortex, owing to the lofting of debris.
ISSN:0027-0644
1520-0493
DOI:10.1175/MWR-D-18-0338.1